Method of cyanide treatment of ores



Patentecl July 2, 1935 q t I v I I UNITED PA ENT 'O F Fl CE F ORES Y Joseph P. Ruth, Jr Denver, c010.

No Drawing. I Application February s, 1933,

- Serial No. 655,389

.7 cla ms; (01. 75-185) This invention relates to improvements in process of vdissolvinggold by cyanide,Iattempted, methodsof-ore treatment and has reference'more by agitation and'aeration, to bring the oxygen: particularly to improvements in the method of content back to theoriginal amount ut. Without yanide treatment of ores. I success. Since there were no active reducing I. 'I have found that a zinc cyanide coating will, sulfides present (they had been coated) I concompletelyv cover all of the sulfide. surfaces when cluded that the u m l y cal reason itis applied-in a solution from which the soluble why the oxygen content couldnot be raised. and air:has been removed. that the diflicultywasnot altogether chemical- 'I- have also found that. sulfides "coated with I concluded that the mass action, of the oxygen;

101 yanide in a de-aerated-solution lose their afpresent was not sufiicient to forcethe reaction finity for air bubbles; andwill not collectin a nec y'tod V t goldl frothas long as'this cyanide coating remains. The coefficient i of absorption for oxygen's'is;

I havealso discovered that sulfides-coated with .04890 andfor nitrogen -023es; (Rosco and zinc cyanide in a de-aerated solution, cannot Schorlemmers Treatis on Chemistry,'5th.Ed.v01.-

METHOD OF GYANIDE TREATMENT '16: readily form oxides in the pulp. when agitated l, pages-312 to 313) this being the case oxygen t with air; r ,The. importance of these discoveries to the cywhich it would not do however. an-ide process of treating .ores is apparent because I have learned-that whena mixture of two gases the cyanide employed in the agitating'and dis is dissolved in' a liquid v(at'a; constant pressure. 1 solving period does not spend itself 'onthe oxides and. temperature) they must reach a definite per of thesulfides which would .be formed in the centand that this amountcannot beincreased absence of t a 1 as long'as the pressure and temperature remain acyanide teston ,an orecontaining mixed the same: 8 sulfides, which had been coated with zinc cyanide In carrying out my cyanide test 'I was using 5 ins. cle-aerated solution, I-expected to get comdissolved oxygen and leaving the nitrogenaand 'plete dissolution of the gold by the cyanide was attempting to replenish the oxygen by 'blow solution, I found, however, that the rapid dising airinto theliquid. Airfas .is well; known, solving action ceased after about :two hours. contains 20% of oxygen, 79% of nitrogen and The :cyanide in solution wasihigh since no oxides 1% of'inert gas, but for the purpose of this specie were formed to consume thecyanide. The exficationwill be considered as being composedof planation of this being that the reducing sul- 20% oxygen and 89% nitrogen. Since the oxygen fides had been coated with zinc cyanide so that and nitrogen are absorbed at different rates but only very little or no cyanicides could form. always in the same ratio, and since the :oxygen I EQther testslha've shown; that, even with the was continually being consumed while thenitroreducing sulfides coated,acritical dissolving point gen was-not consumed, it is evident that the 35 is soon reached at which any further dissolving proportion of oxygen to nitrogen was constantly of gold is accomplished only by agitating .a long decreasing. It isapparentithat the originaliprm time 'withg' air, ,and then in relatively small portions of the two gases can notbe reestablished amounts. Y I by aeration alone. j 1 40 "T s aysdisclosed the presence, of cy Let us assume that water will absorb 4%':by Q

in p e strength d I th refore made further volume of gas and that the oxygen will "form; and careful investigation. 35% thereof, while the nitrogen will form the .From'tests that sl-have madelhave foundithat remainder 0r65%. If the oxygen is now dethe solublesgas containedin-the.cyanidesolution pleted until on1y l5% remains while the nitrogen at the beginning of the treatment consisted of is not removed the quantity of gas will be 30% 35%oxygen and 65% nitrogen, After the v soluofnormal. If we attempt to replace the 20% tion had beenwagitated for periods runningifrom ofeoxygen by blowing air into the'liquid it"will two to ,four hours,'I found that the oxygen conabsorb both oxygen and nitrogen and thexproa tent had been reducedbelowthe normal for tap portion of nitrogen will therefore increase while 59 water. After very long periods of aeration with that of oxygen decreases. It is evident from some :ores I found that as ;much-.as:60% of the thea'bove that after the 'oxygen content has oxygen originally contained' had-been consumed been decreased, it cannot be 'broughtback to audit also discovered-thatnoiamountof aeration the ,original' molecular .concentrationfby' aerawouldincreaseztheioxygencontent- V 1 tion, asfboth oxygen .and nitrogen will be ab- Knowingithat oxygenjisindispensable ithe sorbed. It is possible, however, toemploy oxy'gen should go into solution twice as fast as nitrogen-z gas for this purpose, but this involves a cost that is prohibitive.

I have found that after the oxygen has been depleted beyond the critical point, the molecular concentration can be restored to normal by subjecting the liquid, or pulp, to a vacuum whereby the stabilized oxygen and nitrogen remaining in the liquid are removed. The deaerated solution is now aerated with air and the oxygen and nitrogen will then be absorbed in the proper proportion and the gold will once more go into solution as rapidly as at the beginning of the treatment.

The discovery described above when applied to the cyanide treatment of ores makes it possible to reduce the period of agitation and to take into solution a greater quantity of gold than has heretofore been possible and with a-material reduction in the consumption of cyanide.

The idea of subjecting the pulp to a vacuum after the critical dissolving point has been reached may be made use of practically, in' a number of ways.

The entire pulp may be made to trickle over a lattice work so as to expose a thin film having a large surface and subjecting this film to a vacuum of sufiicient value to remove the oxygen and nitrogen, thus expediting the removal of the dissolved gases. The pulpis then subjected to the usual agitation and aeration. The pulp may be filtered and repulped with water or a water solution, from which the critical gas content has been removed'by a vacuum, and air re-absorbed in the proportion of 35% of oxygen and 15% of nitrogen.

-The method of treatment of ores contemplated may be described as follows:

When the ore is ground with water from which all of the oxygen has been removed by a vacuum treatment and which therefore contains practically no soluble oxygen, the zinc cyanide can be added to the grinding water. Zinc cyanide is formed by combining sodium cyanide with zinc sulfate. If thezinc sulfate is in excess, the zinc cyanide formed will be an insoluble white precipitate. If the cyanide solution is in excess, the zinc cyanide formed will be soluble. Either the insoluble or the soluble zinc cyanide can be used depending on the particular ore under treatment. Many zinc ores contain sufiicient zinc sulfate to form the necessary zinc cyanide when sodium cyanide is added to the pulp.

The amount of sodium cyanide required depends entirely upon what is required'to maintain the standard cyanide solution and this is determined by subjecting' the solution to periodic tests to find the amount of cyanide that has been used or which remains. The amount of cyanide required to reestablish the standard solution is added at any convenient place. That free oxygen is necessary in a cyanide solution for the dissolution of gold is clearly evident from Elsners equation which is as'follows:

After the ore has been ground the pulp is subjected to an agitation period with cyanide until thegold dissolving equilibrium is reached, after which the pulp is subjected to a vacuum treatment which removes from the pulp solution the dissolved gases, which consist principally of nitrogen, and puts the solutionin condition to reabsorb oxygen and nitrogen in their normal proportions; the pulp is now agitated with air whereupon, the oxygen concentration is increased to such an extent that the cyanide action will proceed at its maximum rate.

The step of grinding the ore in oxygen free water can be dispensed with and the ore can be ground in oxygen saturated water or in a cyanide solution, as is the present practice. The step of grinding in oxygen free water is more especially applicable when the ore to be cyanided contains large quantities of reducing sulfides which must be neutralized so that they will not form ferrous sulfides and/or sulphates.

Having described the invention what I claim is: 1. The method of restoring the relative amounts of oxygen and nitrogen to a solution from which a portion of the oxygen has been removed which consists in subjecting the solution to the action of a vacuum of such value that the oxygen and the nitrogen that remains are removed and then aerating the solution whereby the oxygen and nitrogen will be reabsorbed in their normal proportions.

2. The method of restoring the relative amounts of oxygen and nitrogen to a solution from which one of the gases has been removed until the normal proportions have been altered which consists in subjecting the solution to the action of a vacuum of such value that the oxygen and the nitrogen which remains in the solution are removed and then agitating the solution in contact with air whereby oxygen and nitrogen will be reabsorbed in their normal proportions.

3. The method of restoring the relative amounts of oxygen and nitrogen to an ore pulp from which one of the gases has been removed to such an extent as to alter their normal proportions which comprises, subjecting the pulp to the action of a vacuum of such degree and duration that it will remove substantially all of the remaining portions of the oxygen and nitrogen and then agitating the pulp in the presence of air whereby it will reabsorb oxygen and. nitrogen in their'normal proportions.

4. In the method of dissolving gold by the action of cyanide, the steps of replenishing the oxygen content of a pulp in which the oxygen has been reduced to a point below that required for the cyanide reaction which comprises, subjecting the pulp to the action of a vacuum of such value that the oxygen and the nitrogen remaining in solution are removed, and agitating the pulp in contact with air whereby the oxygen and nitrogen will be reabsorbed in their proper proportions.

5. The method of treating ores with cyanide which consists in adding zinc cyanide to the pulp and agitating in the presence of air until the oxygen content of the pulp has been reduced to such an extent that the cyanide reaction substantially ceases, subjecting the pulp to the action of a vacuum of such value that it will remove the remaining quantities of oxygen and nitrogen, continuing the vacuum treatment until these gases are removed and then agitating the pulp in the presence of air whereby oxygen and nitrogen will be reabsorbed in their normal proportions.

6. In the cyanide method of treatment of ores the steps of, grinding the ore with water from which all of the oxygen has been removed, adding zinc cyanide to the grinding water, agitating the ore pulp, so ground, in the presence of air until the equilibrium point of the solubility of gold by the cyanide consumption is reached, subjecting the pulp to a vacuum of such value that it will remove the excess of nitrogen and the remaining oxygen, continuing the vacuum treatment until these gases are removed, and subjecting the degassed pulp to agitation in the presence of air whereby oxygen and nitrogen will be reabsorbed and whereby the dissolving process will be recommenced.

'7. In the cyanide process of the treatment of ores, the steps of, grinding the are in the absence of soluble oxygen and in the presence of zinc cyanide, subjecting the pulp to an agitation period with cyanide whereby gold is dissolved, continuing the agitation until the gold dissolving equilibrium period is reached, subjecting the pulp to a vacuum of sufficient value and duration for removing the dissolved nitrogen, andsubmitting the pulp to a further agitation in contact with air for thereabsorbtion of oxygen and nitrogen in proper proportions and for the further removal of gold.

JOSEPH P. RUTH, JR. 7 

